This invention relates to sensing the presence of bubbles in a liquid, and a particular application thereof is the detection of air bubbles in serum or blood during infusion thereof into a patient. In such procedures it is important to insure that gas or air be prevented from being infused with the liquid, since air emboli can be extremely dangerous in a patient, particularly if the patient is very sick or is a premature or sick newborn.
Various instruments have been developed for preventing air bubbles from being infused into a patient along with a liquid, typical of which are those disclosed is U.S. Pat. Nos. 2,835,252, 3,812,842, 3,935,876 and 4,114,144. Such instruments typically provide an alarm and/or shut off mechanism which is activated when air bubbles are sensed in the infusion liquid being monitored. They may also provide readout means indicating the volume infused up to the cut-off point. Such prior instrumentation commonly suffers from unreliable operation because of low signal level, electronic drift, and/or difficult mechanical alignment.